The present invention relates to a coil winding machine for winding a wire or the like onto a take-up bobbin to fabricate a coil. More particularly, the invention pertains to a coil winding machine for fabricating an optical fiber coil and a coil winding method using the winding machine.
A sensing coil of a fiber optic gyro is usually formed by a multilayer coil so as to provide for enhanced sensitivity. Conventionally, this mutilayer coil has a solenoid-like configuration in which an optical fiber is wound in the opposite direction for each layer as shown in FIG. 1, in which an optical fiber 2 from the one end 2r to the other 2l thereof is wound onto a take-up bobbin B, with a first layer wound from one end to the other of the bobbin B in its axial direction Z as indicated by the arrow 3a, a second layer in the opposite direction as indicated by the arrow 3b. . . .
However, as set forth in N.J. Frigo, SPIE, Vol. 412, pp268-271, 1983, for example, when the senseing coil formed by such a solenoid-like multilayer coil is subjected to a temperature change, its thermometric conductivity variations produce an error in the output of the fiber optic gyro which is expressed by ##EQU1## where n is the refractive index of the optical fiber, N the number of turns, .DELTA.n.sub.0 the product of the temperature coefficient of the refractive index and the temperature changing ratio, and m the number of layers of the coils.
With a view to minimizing the output error of the fiber optic gyro, there has been proposed a sensing coil of a structure in which the one half and the other half of the optical fiber--split in the middle--are alternately wound onto a single take-up bobbin in such a manner that their induvidual parts symmetrical with respect to the middle or intermediate point of the fiber are disposed spatially close or adjacent to each other and are subjected to similar tempertature changes, thereby reducing the contributing factor to the output error.
A variety of coil structures have been proposed to implement such a coil. A typical one of them is such a multilayer coil as depicted in FIG. 2, in which two substantially equal halves of the optical fiber, i.e. the one half portion 2R of the optical fiber 2 from its intermediate point 2c to the one end 2r and the other half portion 2L from the intermediate point 2c to the other end 2l are alternately wound around the take-up bobbin B repeatedly in units of four layers, with the intermediate point 2c held at the innermost position on the bobbin B. A first layer of the coil is formed by winding a part of the one half portion 2R, which is the closest to the intermediate point 2c, around the take-up bobbin B from its one end to the other in its axial direction Z as indicated by the arrow 3c; a second layer is formed by winding a part of the other half portion 2L, which is the closest to the intermediate point 2c, around the bobbin B in the same direction as in the case of the frist layer, as indicated by the arrow 3d; a third layer is formed by winding another part of the other half portion 2L, which is the second closest to the intermediate point 2c, around the bobbin B from the other end to the one end in its axial direction Z as indicated by the arrow 3e; a fourth layer is formed by winding another part of the one half portion 2R, which is the second closest to the intermediate point 2c, around the bobbin B in the same direction as in the case of the third layer, as indicated by the arrow 3f; a fifth layer is formed by winding another part of the one half portion 2R, which is the third closest to the intermediate point 2caround the bobbin B from the one end to the other in its axial direction Z as indicated by the arrow 3g; and the subsequent layers are also formed in the same manner as described above.
With the use of such a multilayer coil, the output error of the fiber optic gyro is marked reduced as compared with the output error suffered in the case of employing th solenoid-like multi-layer coil shown in FIG. 1, as expressed by ##EQU2##
Incidentally, the conventional winding machine is designed exclusively for fabricating the solenoid-like multilayer as depicted in FIG. 1, and hence it cannot be utilized for producing the multilayer coil such as shown in FIG. 2.
According to a conventional method for the manufacture of the multilayer coil depicted in FIG. 2, the one half 2R of the optical fiber 2 from one end 2r to the middle or intermediate point 2c thereof and the other half 2L from the other end 2l to the middle point 2c are wound onto a pair of supply bobbin 4R and 4L through use of a winding machine as shown in FIG. 3, then the middle point 2c of the optical fiber 2 is disposed at the innermost position in the take-up bobbin B, and as shown in FIG. 4, the one half and the other half portions 2R and 2L of the optical fiber 2 are manually wound onto the take-up bobbin B from the supply bobbins 4R and 4L in the sequence and manner described previously with respect to FIG. 2.
However, this prior art method involves handwork as mentioned above, and hence is very time- and labor-consuming. In addition, since the manual winding of the optical fiber 2 onto the take-up bobbin B is subject to each worker's individual difference in skill and concentration on the work, it is difficult to obtain multilayer coils in uniform quality.